Telecommunications equipments are designed to have some means of detecting and reporting traffic-affecting faults. Collecting and displaying these fault alarms is the responsibility of the network Fault Management System (FMS). The functional groups that are the primary users of the FMS are typically called Surveillance, which has responsibility for monitoring equipment faults and initiating repair actions, and Restoration, which has responsibility for rerouting network traffic around an outage.
The alarms generated by network equipments typically identify the affected equipment and the type of fault detected by that equipment. However, a single fault in a network can generate alarm reports throughout the network on any equipment that also transports any of the traffic affected by that fault. It is generally the case that knowledge of network topology (that is, the connections between equipments that define the traffic paths through the network) is not present at the equipment level. Therefore, correlations exist between fault alarm reports that are not immediately obvious without considering the alarms within the context of the network topology.
The following description of the present invention will use the term "circuit" to mean a data traffic carrier or pathway of some specific data capacity through a telecommunications network. Data can only be inserted or retrieved (usually both, since the traffic is two-way) from the end points of this circuit; all other equipments along the path relay the data toward the destination end point.
For efficiency of transmission, multiple circuits of the same capacity are often combined or "multiplexed" together into a single data carrier. This higher-capacity carrier will be called a "trunk", relative to the circuits that is carries. A circuit might be carried by a series of such higher-level trunks on its way to its destination. But each trunk is also a circuit: it provides a specific data-carrying capacity between source and destination end points, and it consists of a series of transmission equipment connections through the network. Trunks of the same capacity can also be multiplexed together to form even higher-level trunks.
The standard digital telecommunications multiplex hierarchy used in the United States consists of: DS-0 circuits (or Digital Signal Level 0) with a capacity of 64 kilobits per second (Kbps); DS-1 circuits of 1.544 megabits per second (Mbps) or 24 DS-0s; DS-2 circuits of 6.312 Mbps or 4 DS-1s; and DS-3 circuits of 44.736 Mbps or 7 DS-2s. Long-haul transmission equipment such as fiber-optic systems combine a certain number of DS-3s, the number being determined by the speed of the specific technology employed. An example would be Synchronous Optical Network (SONET) OC-48 (Optical Carrier Level 48) equipment, which combines 48 DS-3 circuits.
Typically, when a failure occurs on a circuit, the equipment closest to the failure detects the fault ("loss of signal", for example), reports the fault, and propagates an alarm indicator signal in the "downstream" direction on the affected circuit. Alarms are therefore reported in the receive direction on each side of the fault to the far ends of the circuit. Furthermore, if that circuit is a trunk (carrying circuits of a lower capacity level) then the multiplexing equipments at the trunk ends also propagate alarm indicators downstream along those lower-level circuits. As a result, when a major outage occurs a large number of fault alarms are reported. Without considering network topology, it is difficult to determine how many faults there are and which alarms are significant for locating the faults.
Further complicating the situation is the fact that not all equipment connection points provide fault alarm information because of limitations in the equipment (especially older types) or because of limitations within the Fault Management System itself. Moreover, the fault reporting network and remote monitoring subsystems are also subject to failures, so there is always a possibility that some alarms may not be delivered to the Fault Management System.
These complications mean that manual alarm analysis by the FMS users is tedious and time-consuming. This invention is intended to augment the FMS alarm reporting by automating the process of analyzing the transmission equipment alarms in the context of network topology, thereby allowing a faster and more accurate response to a network traffic outage.